<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>实现可以拖动的悬浮框</title>
    <style>
        body{
            height: 100%;
            width: 100%;
            position: relative;
        }
        .btn{
            width: 200px;
            margin: 0 auto;
            text-align: center;
        }
        .main{
            /* 因为下面要用到所以绝对定位 */
            position: absolute;
            left: 50%;
            transform: translate(-50%,0);
            width: 300px;
            height: 300px;
            background-color: skyblue;
            text-align: center;
            line-height: 300px;
            display: none;
            z-index: 100;
        }
        .close-btn{
            position: absolute;
            right: -20px;
            top: -20px;
            width: 50px;
            height: 50px;
            line-height: 50px;
            border-radius: 50%;
            background-color: #ccc;
            color: #ffffff;
        }
        .mask{
            height: 100%;
            width: 100%;
            position: fixed;
            top: 0;
            left: 0;
            background-color: rgba(0, 0, 0, .3);
            display: none;
            z-index: 99;
        }
    </style>
</head>
<body>
    <div class="btn">点击出现悬浮框</div>
    <div class="main">
        <span>这就是出现的悬浮框</span>
        <span class="close-btn">关闭</span>
    </div>
    <div class="mask"></div>
    <script>
        // 获取元素
        let btn=document.querySelector('.btn')
        let main=document.querySelector('.main')
        let closeBtn=document.querySelector('.close-btn')
        let mask=document.querySelector('.mask')
        // 点击显示悬浮框和mask蒙层
        btn.addEventListener('click',function(){
            main.style.display='block'
            mask.style.display='block'
        })
        // 点击隐藏悬浮框和mask蒙层
        closeBtn.addEventListener('click',function(){
            main.style.display='none'
            mask.style.display='none'
        })
        // 鼠标按下
        main.addEventListener('mousedown',function(event){
            // 获得鼠标在盒子里的坐标
            // console.log(event.pageX)
            // console.log(main.offsetLeft)
            let x=event.pageX-main.offsetLeft
            let y=event.pageY-main.offsetTop
            document.addEventListener('mousemove',move)
            // 也可以吧document换成main都行
            function move(event){
                // 盒子距离body的距离=鼠标距离body的距离-鼠标距离盒子的距离
                main.style.left=event.pageX-x+'px'
                main.style.top=event.pageY-y+'px'
            }
            // 鼠标抬起
            document.addEventListener('mouseup',function(){
                document.removeEventListener('mousemove',move)
            })
        })
    </script>
</body>
</html>